1. Technical Field of the Invention
This invention relates generally to water-based printing inks of the type used for newspaper and lithographic printing and in cartridges for ink jet and other computer printers, and more particularly to stable viscous gelled printing ink compositions that contain colorant pigments and other additives in a gel base which prevents separation of the pigments and other additives and imparts improved storage stability while maintaining the desired characteristics of good print quality, water and smear resistance, and light fastness.
2. Brief Description of the Prior Art
Conventional inks are generally composed of a colorant such as carbon black or other colorants as well as additives that increase anti-smudging and ease of use characteristics. Whether the printing is done by offset, letterpress, ink jet or other printing method, all are plagued by the problem of separation of the ink components during storage prior to use.
Carbon black has excellent properties of color and light fastness, however in order to use carbon black in aqueous ink compositions, the carbon black must be dispersed in the medium and then stabilized to prevent separation. Some other pigments also tend to settle and separate during storage
Thus, there is a long-felt need for printing inks to not separate during storage and that are easy to handle and use without having to be shaken, stirred or otherwise mixed prior to use in order to re-suspend the carbon black and other colorants and additives. There is also a continuing need for printing inks that are fast-drying, have improved printability, high color strength, good water balance, and sharp halftone reproduction. These and other desired characteristics can be produced in gelled printing inks that do not separate during storage.
Previous attempts by others to produce storage stable inks include incorporating many ingredients including clays, organo-metalic gelling agents, resins and other polymeric components into the compositions.
Ma, et al, U.S. Pat. No. 5,085,698 discloses a pigmented ink for ink jet printers comprising an aqueous carrier medium, and pigment particles dispersed in an acrylic/acrylate block copolymer serving as a stabilizing agent. The copolymer has a hydrophilic segment and a segment that links to the pigment.
Williams, et al, U.S. Pat. No. 5,844,071 discloses a process for making high viscosity gelled ink resins using a resin conducted through an extruder with a cross-linking agent, preferably a heat reactive phenolic resin, to produce a high viscosity resin that resists viscosity breakdown under high shear conditions. The resulting gelled ink resins may be used directly in making ink obviating the need for further gelation and avoiding the use of conventional organio-metallic gelling agents.
Beach, et al, U.S. Pat. No. 5,869,564 discloses an aqueous ink composition with improved storage stability for use in ink jet printers comprising an aqueous carrier; a pigment; and a copolymer comprising a hydrophilic segment having an acidic function group, and a hydrophobic segment having a hydrolytically stable siloxyl substituent.
The present invention overcomes the problems discussed above and is distinguished over the prior art in general and these patents in particular, by a stable viscous gelled printing ink composition wherein colorants, pigments, and other property enhancing additives are dispersed in a water-based gel carrier to provide a smooth viscous homogeneous stable printing ink gel having the consistency of a custard or jelly. The stabilized gel prevents separation and settling of the homogeneously suspended colorants, pigments, and property enhancing additives, and significantly improves storage stability. The ink compositions do riot require shaking, stirring, or mixing prior to use, are fast drying on paper, and do not dry on the printing press, in the storage containers, or in the ink jet or bubble jet injector nozzles. The gelled ink compositions with property enhancing additives also have improved non rub-off characteristics, excellent printability, high color strength, good water balance, less mist, and sharp halftone reproduction.
It is therefore an object of the present invention to provide a stable viscous gelled printing ink composition wherein there is no-separation or settling of the colorants, pigments, and property enhancing additives, and thus has excellent storage stability and long shelf life.
It is another object of this invention to provide a printing ink composition wherein colorants, pigments, and other property enhancing additives are homogeneously suspended in a smooth stable viscous gel having the consistency of a custard or jelly.
Another object of this invention is to provide a smooth stable viscous gelled printing ink composition which does not require shaking , stirring, or mixing prior to use.
Another object of this invention is to provide a smooth stable viscous gelled printing ink composition which is fast drying on paper, but does not dry on the printing press, in the storage containers, or in the ink jet or bubble jet injector nozzles.
A further object of this invention is to provide a smooth stable viscous gelled printing ink composition having homogeneously suspended colorants, pigments, and property enhancing additives, that has improved non rub-off characteristics, excellent printability, high color strength, good water balance, less mist, and sharp halftone reproduction.
Other objects of the invention will become apparent from time to time throughout the specification and claims as hereinafter related.
The above noted objects and other objects of the invention are accomplished by a smooth stable viscous gelled printing ink composition comprising a mixture of water, a gelling agent, a chelating agent, and a colorant or pigment, property enhancing additives evenly dispersed into the mixture, and an alkaline electrolyte viscosity increasing agent that raises the pH of the mixture and forms a smooth homogeneous stable gel with a viscosity level having the consistency of a custard or jelly.